: The CCAAT/enhancer binding protein alpha (C/EBPa) is responsible for the activation of many adipose-specific genes in adipocytes. An isoform of activator protein-2a (AP-2a) has been implicated as a repressor of C/EBPa transcription in preadipocytes, binding to C/EBPa Undifferentiated Protein (CUP) sites within the promoter of the gene. Toward the goal of identifying the mechanism of repression of adipogenesis, the specific aims of the proposal are: 1) To identify the AP-2a iso form responsible for C/EBPa repression in 3T3-L1 preadipocytes, 2) To identify and characterize other proteins involved in the CUP-repressor complex. 3) To characterize the effects of AP-2a expression on differentiation using both ex vivo and in vivo systems. RT-PCR and reporter assays will be used to identify the AP-2a isoform responsible for C/EBPa repression. Yeast two-hybrid assays will be used to identify proteins which interact with AP-2a, including a candidate 32 kD protein. The function of AP-2cx in preadipocytes during the differentiation program will be examined with an inducible retroviral expression system using both cell culture and an in vivo implantation technique. Completion of the proposed research will contribute toward understanding repression of adipogenesis and may serve as a starting point for manipulation of the adipogenic process in the treatment of obesity and obesity-associated illnesses.